The process and advantages of gasifying hydrocarbonaceous material into synthesis gas, or syngas, are generally known in the industry. In high temperature gasification processes, synthesis gas is commonly produced from gaseous combustible fuels, such as natural gas, and solid combustible organic fuels, such as coal, residual petroleum, wood, tar sand, shale oil, and municipal, agriculture or industrial waste. The gaseous or solid combustible organic fuels are reacted with a reactive oxygen-containing gas, such as air, enriched air, or pure oxygen, and a temperature modifier, such as steam, in a gasification reactor to obtain the synthesis gas.
In a typical gasification process, the synthesis gas will substantially comprise hydrogen (H2), carbon monoxide (CO), and lessor quantities of impurities, such as water (H2O), carbon dioxide (CO2), carbonyl sulfide (COS) and hydrogen sulfide (H2S). The synthesis gas is commonly treated to remove or significantly reduce the quantity of impurities, particularly H2S, COS, and CO2 before being utilized in a downstream process. A number of acid gas removal systems are commercially available and selection will depend on the degree of sulfur compounds and carbon dioxide removal required by the process and the operating pressure of the acid gas removal system.
The hydrogen can then be harvested from the synthesis gas and used as an excess reactant in a hydroprocessing unit. Hydroprocessing covers various refinery operations, including, but not limited to, catalytic desulfurization, denitrification, hydrotreating to remove other contaminants, pretreatment of reformer feedstocks, and hydrocracking to break down heavy hydrocarbon materials. The remaining components of the syngas, primarily carbon monoxide and a small portion of hydrogen, can then be consumed in a combustion turbine for power production.
The hydrocracking unit is the most versatile of refinery conversion units. It can process a wide range of feedstocks from naphtha to asphalt to yield any desired product with a molecular weight lower than that of the feedstock. Hydrotreating is the most widely used catalytic refinery process and can treat feedstocks from the lightest naphthas to the heaviest vacuum resids. It is used primarily to remove undesired impurities, such as sulfur containing compounds, from the feedstocks. Both hydrocracking and hydrotreating utilize hydrogen as a reactant. Catalytic cracking is similar to hydrocracking, except that no hydrogen is used. In each process, a catalyst is used which can become deactivated by any metal or solid impurities found in the feedstock, as well as by any coke produced in the process.
Because the hydrogen is usually fed to the hydroprocessing unit in excess, hydrogen is present in the product stream of the unit. It is desirable to recover this hydrogen for recycle back to the inlet of the hydroprocessing unit. Due to pressure reductions in the hydrogen during processing, though, the hydrogen needs to be compressed for recycle back to the hydroprocessing unit. Thus, it would be desirable to develop an economical process to boost the hydrogen pressure for use as a recycle stream.